Water and wastewater are commonly treated using a variety of techniques. Many conventional municipal and industrial wastewater treatment plants utilize lagoon technologies in treating wastewater. FIG. 1 illustrates a commonly known prior art lagoon system 10 comprising multiple lagoon basins 12 and 14 in series. In many cases, these lagoon technologies are advantageous over alternative options because they require only minimal operator attention, they can be operated by a lower-class operator, and they require a relatively small amount of mechanical equipment. These lagoon technologies are typically capable of minimizing sludge handling procedures; however, such lagoon technologies are not without shortcomings, particularly in providing advanced treatment for wastewater in cold weather when nitrification or nutrient control is desired.
Lagoons have demonstrated excellent capability for biochemical oxygen demand (BOD) removal in all seasons and even nitrification and in some cases de-nitrification in warm weather climates where temperatures are elevated in the lagoon basins. In cold weather, the biological organisms used for executing nitrification and de-nitrification in the lagoons become less effective once the wastewater temperature drops below a certain level, for example, about 8° C. or 10° C. or lower. Once the wastewater temperature drops to these levels, the biological organisms are often not able to undertake full nitrification or de-nitrification in lagoons at these cooler temperatures and the lagoon process has limited control that can be used to improve performance. Synthesis or growth activity of nitrification biological organisms in particular is minimized at these cooler temperatures. Since lagoons typically have a large surface area to volume ratio, wastewater fed into the lagoons often cools rapidly when the ambient air temperature is relatively cold. This loss in basin temperature has an adverse impact on the treatment of the water for carbonaceous BOD removal, but nitrification and de-nitrification activity simply ceases at those lowered lagoon temperatures. Once the biosolids for nitrification and de-nitrification are lost, they are difficult or impossible to re-establish, in the lagoons until warmer weather.
To overcome the limitations of the lagoon system not being able to perform the proper treatment at the lower temperatures, high rate biological reactors have been used in place of lagoons. These high rate biological reactors are quite effective in controlling the variables, as their smaller volume retains heat to maintain basin temperatures in the proper zone for nitrification and nutrient control, as well as carbonaceous BOD removal. In addition, the high rate systems typically have a means for greatly increasing the biomass population through either suspended growth or fixed growth mechanisms and the high population of biomass can serve as a buffer and a treatment biomass even during cold weather temperatures. High rate systems that are properly operated and managed, can deliver the necessary BOD removal and treatment, as well as the necessary nutrient control and removal.
In many of the currently known high rate treatment system technologies, the entire flow of wastewater flowing into the reactor must be treated on a continuous basis. The rate at which the wastewater arrives at the treatment plant often varies dramatically throughout the day and varies even more dramatically during wet weather and storm events. In communities where the separation between sanitary sewer and storm water runoff sewer has become compromised and in communities having a combined sewer system, excessive flow may result at the treatment plant during such wet weather or storm events. Each successive flow event results in a spike in the volumetric flow rate of wastewater that must be treated by the high rate reactor. The high rate reactor is designed to handle a specific volumetric flow rate (QR). The rate of flow of wastewater into this high rate reactor during a storm event can reach a volumetric flow rate as much as 10 times greater (i.e., 10QR) than the normal design volumetric flow rate QR. These larger volumetric flow rates put tremendous stress on the high rate reactor and can seriously impact the performance of the wastewater treatment process.
In the prior lagoon systems, the very large volume of the lagoon adequately managed hydraulic flow variation. However, prior lagoons could not deliver the treatment levels necessary as described above and, therefore, the high rate systems are required. The high rate systems must have hydraulic management in order to assure their performance. A flush out or elutriation of the accumulated nitrification and de-nitrification organisms and loss in performance is common in these biological high rate reactors in cold weather storm or high flow events. This loss of biomass may result in a violation of effluent water quality regulations set by a regulatory agency, such as the Environmental Protection Agency (EPA), during the remainder of the cold weather, i.e., until the spring season warm-up.
Accordingly a need exists for a system and method adapted for both managing the flow of wastewater into a reactor and directing the wastewater into the reactor during periods of time when the biological reaction rates within the reactor assure proper treatment, particularly for nitrification and de-nitrification. A need also exists for a system and method for a use of an existing lagoon wastewater treatment basin to function as an influent flow equalization basin in conjunction with a wastewater treatment system including a high rate biological reactor. A further need exists for a system and method for a wastewater treatment system having an integrated control system that redirects wastewater stored in an influent flow equalization basin to a reactor only when (a) the temperature of the wastewater being stored in the influent flow equalization basin is greater than or equal to a predetermined temperature and (b) wastewater is received by the wastewater treatment system at a rate less than a predetermined flow rate.